1. Field of the Invention
The present invention relates to magneto-resistive sensing devices for position measurement and, more particularly, to a contactless magneto-resistive angular position sensing device with a temperature-stable zero point that produces an output signal according to its angular position in an applied magnetic field.
2. Prior Art
It is known to use magneto-resistive sensors for contactless detection of changes in state, for instance for measuring an angular position of a rotatably mounted part. Such magneto-resistive sensors typically include magnet-field-dependent resistors which are connected in a bridge, and through which a control current that is fed to a bridge diagonal flows.
When such a magneto-resistive sensor is influenced by a magnetic field, a voltage is established at the other bridge diagonal, the magnitude of the voltage depending on the magnetic field or on the direction of the magnetic field referred to the sensor. The relationship between the bridge voltage and the magnetic field direction is utilized in a contactless AMR (Anisotropic Magneto Resistance) angle encoder for detecting measurement values. If precise measurement is to be possible at all, a zero point must first be defined, or a calibration of the sensor must be performed.
From Published, Non-Examined German Patent Application DE-OS 43 364 82, a method for calibrating a magneto-resistive sensor is known with which the offset error can be compensated for. To that end, the magneto-resistive sensor, which is constructed as a bridge circuit, is acted upon by a homogeneous magnetic field oriented in a definite way, and a definite control current is applied to the current contacts of the bridge circuit. The voltage that is then established at the other contacts is measured on an ongoing basis. The magneto-resistive sensor is processed with the aid of a laser until such time as the offset voltage when the magnetic field is applied becomes equal to zero.